Magnetization is possible of certain materials, it is possible to find out discontinuities by using the medium (iron powder) having the magnetic attraction. Magnetic Particle Inspection is relatively easy and simple test method that can be applied at various stages of manufacturing and process.

The direction is more impartment factor than the magnitude of magnetizing current. For reliable magnetic particle inspection, magnetic lines should be perpendicular to the discontinuity. If magnetic lines are parallel to the discontinuity then leakage will be little and indications will be small or indefinite.

Cracks distort the magnetic lines of force and create poles on either side of the crack. Strength depends upon the number of interrupted lines of force. Indications of maximum size are found when magnetic lines are at right angle to discontinuities. The Intensity of magnetization depends upon the susceptibility of material to become magnetized